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Kremer AN, Bausenwein J, Lurvink E, Kremer AE, Rutten CE, van Bergen CAM, Kretschmann S, van der Meijden E, Honders MW, Mazzeo D, Watts C, Mackensen A, Falkenburg JHF, Griffioen M. Discovery and Differential Processing of HLA Class II-Restricted Minor Histocompatibility Antigen LB-PIP4K2A-1S and Its Allelic Variant by Asparagine Endopeptidase. Front Immunol 2020; 11:381. [PMID: 32218783 PMCID: PMC7078166 DOI: 10.3389/fimmu.2020.00381] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Accepted: 02/17/2020] [Indexed: 12/03/2022] Open
Abstract
Minor histocompatibility antigens are the main targets of donor-derived T-cells after allogeneic stem cell transplantation. Identification of these antigens and understanding their biology are a key requisite for more insight into how graft vs. leukemia effect and graft vs. host disease could be separated. We here identified four new HLA class II-restricted minor histocompatibility antigens using whole genome association scanning. For one of the new antigens, i.e., LB-PIP4K2A-1S, we measured strong T-cell recognition of the donor variant PIP4K2A-1N when pulsed as exogenous peptide, while the endogenously expressed variant in donor EBV-B cells was not recognized. We showed that lack of T-cell recognition was caused by intracellular cleavage by a protease named asparagine endopeptidase (AEP). Furthermore, microarray gene expression analysis showed that PIP4K2A and AEP are both ubiquitously expressed in a wide variety of healthy tissues, but that expression levels of AEP were lower in primary acute myeloid leukemia (AML). In line with that, we confirmed low activity of AEP in AML cells and demonstrated that HLA-DRB1*03:01 positive primary AML expressing LB-PIP4K2A-1S or its donor variant PIP4K2A-1N were both recognized by specific T-cells. In conclusion, LB-PIP4K2A-1S not only represents a novel minor histocompatibility antigen but also provides evidence that donor T-cells after allogeneic stem cell transplantation can target the autologous allelic variant as leukemia-associated antigen. Furthermore, it demonstrates that endopeptidases can play a role in cell type-specific intracellular processing and presentation of HLA class II-restricted antigens, which may be explored in future immunotherapy of AML.
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Affiliation(s)
- Anita N Kremer
- Department of Internal Medicine 5, Hematology/Oncology, Friedrich Alexander University Erlangen-Nuremberg, Erlangen, Germany
| | - Judith Bausenwein
- Department of Internal Medicine 5, Hematology/Oncology, Friedrich Alexander University Erlangen-Nuremberg, Erlangen, Germany
| | - Ellie Lurvink
- Department of Hematology, Leiden University Medical Center, Leiden, Netherlands
| | - Andreas E Kremer
- Department of Internal Medicine 1, Gastroenterology, Pneumology and Endocrinology, Friedrich Alexander University Erlangen-Nuremberg, Erlangen, Germany
| | - Caroline E Rutten
- Department of Hematology, Leiden University Medical Center, Leiden, Netherlands
| | | | - Sascha Kretschmann
- Department of Internal Medicine 5, Hematology/Oncology, Friedrich Alexander University Erlangen-Nuremberg, Erlangen, Germany
| | - Edith van der Meijden
- Department of Internal Medicine 5, Hematology/Oncology, Friedrich Alexander University Erlangen-Nuremberg, Erlangen, Germany
| | - Maria W Honders
- Department of Hematology, Leiden University Medical Center, Leiden, Netherlands
| | - Daniela Mazzeo
- Division of Cell Signaling & Immunology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Colin Watts
- Division of Cell Signaling & Immunology, School of Life Sciences, University of Dundee, Dundee, United Kingdom
| | - Andreas Mackensen
- Department of Internal Medicine 5, Hematology/Oncology, Friedrich Alexander University Erlangen-Nuremberg, Erlangen, Germany
| | | | - Marieke Griffioen
- Department of Hematology, Leiden University Medical Center, Leiden, Netherlands
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Pont MJ, Oostvogels R, van Bergen CA, van der Meijden ED, Honders MW, Bliss S, Jongsma ML, Lokhorst HM, Falkenburg JF, Mutis T, Griffioen M, Spaapen RM. T Cells Specific for an Unconventional Natural Antigen Fail to Recognize Leukemic Cells. Cancer Immunol Res 2019; 7:797-804. [DOI: 10.1158/2326-6066.cir-18-0137] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Revised: 12/21/2018] [Accepted: 03/14/2019] [Indexed: 11/16/2022]
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van der Lee DI, Reijmers RM, Honders MW, Hagedoorn RS, de Jong RC, Kester MG, van der Steen DM, de Ru AH, Kweekel C, Bijen HM, Jedema I, Veelken H, van Veelen PA, Heemskerk MH, Falkenburg JHF, Griffioen M. Mutated nucleophosmin 1 as immunotherapy target in acute myeloid leukemia. J Clin Invest 2019; 129:774-785. [PMID: 30640174 DOI: 10.1172/jci97482] [Citation(s) in RCA: 112] [Impact Index Per Article: 22.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Accepted: 11/06/2018] [Indexed: 12/15/2022] Open
Abstract
The most frequent subtype of acute myeloid leukemia (AML) is defined by mutations in the nucleophosmin 1 (NPM1) gene. Mutated NPM1 (ΔNPM1) is an attractive target for immunotherapy, since it is an essential driver gene and 4 bp frameshift insertions occur in the same hotspot in 30%-35% of AMLs, resulting in a C-terminal alternative reading frame of 11 aa. By searching the HLA class I ligandome of primary AMLs, we identified multiple ΔNPM1-derived peptides. For one of these peptides, HLA-A*02:01-binding CLAVEEVSL, we searched for specific T cells in healthy individuals using peptide-HLA tetramers. Tetramer-positive CD8+ T cells were isolated and analyzed for reactivity against primary AMLs. From one clone with superior antitumor reactivity, we isolated the T cell receptor (TCR) and demonstrated specific recognition and lysis of HLA-A*02:01-positive ΔNPM1 AML after retroviral transfer to CD8+ and CD4+ T cells. Antitumor efficacy of TCR-transduced T cells was confirmed in immunodeficient mice engrafted with a human AML cell line expressing ΔNPM1. In conclusion, the data show that ΔNPM1-derived peptides are presented on AML and that CLAVEEVSL is a neoantigen that can be efficiently targeted on AML by ΔNPM1 TCR gene transfer. Immunotherapy targeting ΔNPM1 may therefore contribute to treatment of AML.
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Affiliation(s)
| | | | | | | | | | | | | | - Arnoud H de Ru
- Center for Proteomics and Metabolomics, Leiden University Medical Center, Leiden, Netherlands
| | | | | | | | | | - Peter A van Veelen
- Center for Proteomics and Metabolomics, Leiden University Medical Center, Leiden, Netherlands
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Pont MJ, van der Lee DI, van der Meijden ED, van Bergen CAM, Kester MGD, Honders MW, Vermaat M, Eefting M, Marijt EWA, Kielbasa SM, Hoen PAC', Falkenburg JHF, Griffioen M. Integrated Whole Genome and Transcriptome Analysis Identified a Therapeutic Minor Histocompatibility Antigen in a Splice Variant of ITGB2. Clin Cancer Res 2016; 22:4185-96. [PMID: 26964570 DOI: 10.1158/1078-0432.ccr-15-2307] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Accepted: 02/29/2016] [Indexed: 11/16/2022]
Abstract
PURPOSE In HLA-matched allogeneic hematopoietic stem cell transplantation (alloSCT), donor T cells recognizing minor histocompatibility antigens (MiHAs) can mediate desired antitumor immunity as well as undesired side effects. MiHAs with hematopoiesis-restricted expression are relevant targets to augment antitumor immunity after alloSCT without side effects. To identify therapeutic MiHAs, we analyzed the in vivo immune response in a patient with strong antitumor immunity after alloSCT. EXPERIMENTAL DESIGN T-cell clones recognizing patient, but not donor, hematopoietic cells were selected for MiHA discovery by whole genome association scanning. RNA-sequence data from the GEUVADIS project were analyzed to investigate alternative transcripts, and expression patterns were determined by microarray analysis and qPCR. T-cell reactivity was measured by cytokine release and cytotoxicity. RESULTS T-cell clones were isolated for two HLA-B*15:01-restricted MiHA. LB-GLE1-1V is encoded by a nonsynonymous SNP in exon 6 of GLE1 For the other MiHAs, an associating SNP in intron 3 of ITGB2 was found, but no SNP disparity was present in the normal gene transcript between patient and donor. RNA-sequence analysis identified an alternative ITGB2 transcript containing part of intron 3. qPCR demonstrated that this transcript is restricted to hematopoietic cells and SNP-positive individuals. In silico translation revealed LB-ITGB2-1 as HLA-B*15:01-binding peptide, which was validated as hematopoietic MiHA by T-cell experiments. CONCLUSIONS Whole genome and transcriptome analysis identified LB-ITGB2-1 as MiHAs encoded by an alternative transcript. Our data support the therapeutic relevance of LB-ITGB2-1 and illustrate the value of RNA-sequence analysis for discovery of immune targets encoded by alternative transcripts. Clin Cancer Res; 22(16); 4185-96. ©2016 AACR.
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Affiliation(s)
- Margot J Pont
- Department of Hematology, Leiden University Medical Center, Leiden, the Netherlands
| | | | | | | | - Michel G D Kester
- Department of Hematology, Leiden University Medical Center, Leiden, the Netherlands
| | - Maria W Honders
- Department of Hematology, Leiden University Medical Center, Leiden, the Netherlands
| | - Martijn Vermaat
- Department of Human Genetics, Leiden University Medical Center, Leiden, the Netherlands
| | - Matthias Eefting
- Department of Hematology, Leiden University Medical Center, Leiden, the Netherlands
| | - Erik W A Marijt
- Department of Hematology, Leiden University Medical Center, Leiden, the Netherlands
| | - Szymon M Kielbasa
- Department of Medical Statistics and Bioinformatics, Leiden University Medical Center, Leiden, the Netherlands
| | - Peter A C 't Hoen
- Department of Human Genetics, Leiden University Medical Center, Leiden, the Netherlands
| | | | - Marieke Griffioen
- Department of Hematology, Leiden University Medical Center, Leiden, the Netherlands.
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Pont MJ, Hobo W, Honders MW, van Luxemburg-Heijs SAP, Kester MGD, van Oeveren-Rietdijk AM, Schaap N, de Boer HC, van Bergen CAM, Dolstra H, Falkenburg JHF, Griffioen M. LB-ARHGDIB-1R as a novel minor histocompatibility antigen for therapeutic application. Haematologica 2015; 100:e419-22. [PMID: 26069289 DOI: 10.3324/haematol.2015.125021] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Affiliation(s)
- Margot J Pont
- Department of Hematology, Leiden University Medical Center, Nijmegen, the Netherlands
| | - Willemijn Hobo
- Department of Laboratory Medicine, Radboud University Medical Center, Nijmegen
| | - Maria W Honders
- Department of Hematology, Leiden University Medical Center, Nijmegen, the Netherlands
| | | | - Michel G D Kester
- Department of Hematology, Leiden University Medical Center, Nijmegen, the Netherlands
| | - Annemarie M van Oeveren-Rietdijk
- Department of Nephrology and the Einthoven Laboratory for Experimental Vascular Medicine, Leiden University Medical Center, Nijmegen, the Netherlands
| | - Nicolaas Schaap
- Department of Hematology, Radboud University Medical Center, Nijmegen, the Netherlands
| | - Hetty C de Boer
- Department of Nephrology and the Einthoven Laboratory for Experimental Vascular Medicine, Leiden University Medical Center, Nijmegen, the Netherlands
| | | | - Harry Dolstra
- Department of Laboratory Medicine, Radboud University Medical Center, Nijmegen
| | | | - Marieke Griffioen
- Department of Hematology, Leiden University Medical Center, Nijmegen, the Netherlands
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Veuger MJ, Honders MW, Landegent JE, Willemze R, Barge RM. A novel RT-PCR-based protein activity truncation assay for direct assessment of deoxycytidine kinase in small numbers of purified leukemic cells. Leukemia 2000; 14:1678-84. [PMID: 10995016 DOI: 10.1038/sj.leu.2401880] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
In vitro studies have demonstrated that deoxycytidine kinase (dCK) plays a crucial role in the mechanism of resistance to cytarabine (AraC). The resistant phenotype in vitro is always a result of mutational inactivation of dCK, leading to defects in the metabolic pathways of AraC. Although inactivation of dCK has shown to be one of the major mechanism of resistance to AraC in vitro, limited in vivo data are available. To improve research concerning the involvement of dCK inactivation in patients with acute myeloid leukemia (AML), we have set up a protocol that allows direct assessment of dCK expression and activity in primary human cells. In this protein activity truncation assay (PAT assay), the complete coding region of dCK is amplified by RT-PCR and a T7 RNA polymerase promoter sequence is introduced upstream of the coding region in a nested PCR reaction. After in vitro transcription-translation dCK proteins are analyzed for their molecular weight and phosphorylating capacities. We show that this relatively quick method can be used in purified, primary human leukemic blasts. In addition, inactivation of dCK by point mutations, deletions or genomic rearrangements can easily be detected in AraC-resistant cell lines. This novel assay may contribute to further elucidate the mechanism of AraC resistance in vivo.
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Affiliation(s)
- M J Veuger
- Department of Hematology, Leiden University Medical Center, The Netherlands
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Veuger MJ, Honders MW, Landegent JE, Willemze R, Barge RM. High incidence of alternatively spliced forms of deoxycytidine kinase in patients with resistant acute myeloid leukemia. Blood 2000; 96:1517-24. [PMID: 10942400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023] Open
Abstract
Deficiency of functional deoxycytidine kinase (dCK) is a common characteristic for in vitro resistance to cytarabine (AraC). To investigate whether dCK is also a target for induction of AraC resistance in patients with acute myeloid leukemia (AML), we determined dCK messenger RNA (mRNA) expression in (purified) leukemic blasts and phytohemagglutinin-stimulated T cells (PHA T cells) from patients with chemotherapy-sensitive and chemotherapy-resistant AML. In control samples from healthy donors (PHA T cells and bone marrow), only wild-type dCK complementary DNA (cDNA) was amplified. Also, in (purified) leukemic blasts from patients with sensitive AML, only wild-type dCK cDNAs were observed. These cDNAs coded for active dCK proteins in vitro. However, in 7 of 12 (purified) leukemic blast samples from patients with resistant AML, additional polymerase chain reaction fragments with a deletion of exon 5, exons 3 to 4, exons 3 to 6, or exons 2 to 6 were detected in coexpression with wild-type dCK. Deletion of exons 3 to 6 was also identified in 6 of 12 PHA T cells generated from the patients with resistant AML. The deleted dCK mRNAs were formed by alternative splicing and did code for inactive dCK proteins in vitro. These findings suggest that the presence of inactive, alternatively spliced dCK mRNA transcripts in resistant AML blasts may contribute to the process of AraC resistance in patients with AML. (Blood. 2000;96:1517-1524)
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Affiliation(s)
- M J Veuger
- Laboratory of Experimental Hematology, Department of Hematology, Leiden University Medical Center, Leiden, The Netherlands
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8
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Stegmann AP, Honders MW, Hagemeijer A, Hoebee B, Willemze R, Landegent JE. In vitro-induced resistance to the deoxycytidine analogues cytarabine (AraC) and 5-aza-2'-deoxycytidine (DAC) in a rat model for acute myeloid leukemia is mediated by mutations in the deoxycytidine kinase (dck) gene. Ann Hematol 1995; 71:41-7. [PMID: 7543292 DOI: 10.1007/bf01696231] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The deoxycytidine kinase (dck) gene encodes the enzyme responsible for the metabolic activation of the antileukemic drugs cytosine arabinoside (AraC) and 5-aza-2'-deoxycytidine (decitabine, DAC). The dck locus was analyzed at the chromosomal and the molecular level in a model of rat leukemic cell lines, in which AraC and DAC resistance was induced, that was marked by dck deficiency. At the chromosomal level, karyotype analysis of metaphase spreads revealed the presence of an aberrant 2q + chromosome in the AraC-resistant cell line and a (Xq:11q) translocation in its subclone RA/7. The DAC-resistant lines were identical to the parental RCL/O. Fluorescence in situ hybridization on normal rat fibroblast metaphase spreads localized the rat dck gene to chromosome 14q21-q22, a region that was not involved in any of the observed karyotypic aberrations. Analysis at the molecular level revealed an identical rearrangement of the dck gene in the AraC-resistant cell line RCL/A and its subclone RA/7 that resulted in the absence of dck expression, as assessed by RT-PCR. No genomic rearrangements were observed in a DAC-resistant cell line RCL/D or in its subclone RD/1. However, detection of a single-stranded conformation polymorphism (SSCP) allowed the identification of a single C to G substitution (His to Gln) in the dck cDNA of the DAC-resistant RD/1 clone. The data demonstrate that exposure to AraC and DAC induces a resistant phenotype marked by functional dck deficiency that may be the consequence of mutations occurring in the dck gene.
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MESH Headings
- Animals
- Antineoplastic Agents/pharmacology
- Azacitidine/analogs & derivatives
- Azacitidine/pharmacology
- Base Sequence
- Chromosome Aberrations
- Cytarabine/pharmacology
- Decitabine
- Deoxycytidine Kinase/genetics
- Drug Resistance/genetics
- In Situ Hybridization, Fluorescence
- Leukemia, Myeloid, Acute/drug therapy
- Leukemia, Myeloid, Acute/enzymology
- Leukemia, Myeloid, Acute/genetics
- Molecular Sequence Data
- Point Mutation
- Polymorphism, Single-Stranded Conformational
- Rats
- Translocation, Genetic
- Tumor Cells, Cultured
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Affiliation(s)
- A P Stegmann
- University of North Carolina at Chapel Hill, Department of Pharmacology 27599, USA
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Stegmann AP, Honders MW, Willemze R, Landegent JE. De novo induced mutations in the deoxycytidine kinase (dck) gene in rat leukemic clonal cell lines confer resistance to cytarabine (AraC) and 5-aza-2'-deoxycytidine (DAC). Leukemia 1995; 9:1032-8. [PMID: 7541096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
We have investigated whether cytarabine (AraC) or decitabine (DAC) induce deficiency of deoxycytidine kinase (DCK) through different mutations of the dck gene, related to their distinct interference with DNA replication. Also, it is not known whether mutations of the dck gene are the result of selection of mutants or de novo induction. To address these issues, three subclones of a rat leukemic cell line (RCL/O), sensitive to cytotoxicity mediated by AraC and DAC, were exposed to gradually increasing concentrations (from 0.1 to 10 microM) of either AraC or DAC over a 140 days vs a 180 days period. During the course of resistance induction DCK activity was monitored. We found that all clones acquired irreversible cross-resistance, at marginally cytotoxic AraC or DAC concentrations of 0.1 to 0.4 times the IC50 for the parental clones. Furthermore, all resistant cell lines were DCK deficient and harbored different mutations in the dck gene. AraC induced both rearrangements and point mutations in the dck gene when administered over 140 days and 180 days, respectively. 140 days DAC induction yielded point mutations only. All point mutations detected were nonrandomly distributed within the dck coding region. SSCP analysis showed that in the majority of resistant clones more than one bandshift was present. The data suggest the presence of multiple resistant clones, originating from one sensitive clone and thus arguing against selection of mutants as a mechanism for the development of AraC and DAC resistance.
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Affiliation(s)
- A P Stegmann
- Department of Hematology, University Hospital Leiden, The Netherlands
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10
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Abstract
In order to study the mutational inactivation of deoxycytidine kinase (Dck) in a rat model for acute myeloid leukemia we have cloned the complete coding region of the rat Dck gene. Using primers chosen from the human Dck cDNA sequence, we obtained a rat-specific probe via PCR and used it to isolate two clones from a rat lymphocyte cDNA library. The ORF showed 89.7 and 92.2% nucleotide identity with the human and mouse Dck, respectively, and encodes a 260-amino-acid protein, that is 91.9 and 94.6% homologous to human and mouse Dck, respectively. Northern blot analysis of rat tissues revealed high expression of a 4.1-kb Dck transcript in the thymus, whereas spleen, liver and lung samples showed weak expression of the gene. This tissue-specific expression pattern was confirmed by cDNA-PCR analysis.
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Affiliation(s)
- A P Stegmann
- Laboratory for Experimental Hematology, University Hospital Leiden, The Netherlands
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11
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Stegmann AP, Honders MW, Bolk MW, Wessels J, Willemze R, Landegent JE. Assignment of the human deoxycytidine kinase (DCK) gene to chromosome 4 band q13.3-q21.1. Genomics 1993; 17:528-9. [PMID: 8406512 DOI: 10.1006/geno.1993.1365] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- A P Stegmann
- Department of Hematology, Sylvius Laboratories, University of Leiden, The Netherlands
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12
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Stegmann AP, Honders MW, Kester MG, Landegent JE, Willemze R. Role of deoxycytidine kinase in an in vitro model for AraC- and DAC-resistance: substrate-enzyme interactions with deoxycytidine, 1-beta-D-arabinofuranosylcytosine and 5-aza-2'-deoxycytidine. Leukemia 1993; 7:1005-11. [PMID: 7686601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Deoxycytidine kinase activity (dCk) was monitored in cell lines from a rat acute myeloid leukemia model of acquired resistance to cytosine arabinoside (AraC) and decitabine (DAC). In both AraC-resistant cell lines (RCL/A and its subclone RA/7), as well as in a DAC-resistant cell line (RCL/D) which we generated from the drug-sensitive RCL/0 cell line, a total deficiency of dCk activity and a cross-resistance for AraC and DAC was demonstrated. Furthermore, the metabolization of deoxycytidine (dC) was severely impaired in all these cell lines. Km values for dC (9.4 microM in RCL/0 cells) had increased 70- to 100-fold in RCL/D (Km = 673.2 microM), in RCL/A (Km = 947.2 microM) and in RA/7 (Km = 817.5 microM). Vmax values were unaltered in RCL/D and RA/7, and twofold increased in RCL/A. Addition of hydroxyurea (HU) to cell cultures stimulated dCk salvage pathway activity in RCL/0 cells for dC, AraC, and DAC by increasing Vmax values approximately 160% leaving Km constants unchanged. In all resistant cell lines, HU pre-incubation did not influence the level of dCk activity, leaving Km and Vmax values unaltered. These data indicate that deficiency of dCk activity is crucial in the mechanism of drug resistance in this model.
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Affiliation(s)
- A P Stegmann
- Department of Hematology, University Hospital Leiden, The Netherlands
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